1. Field of the Invention
The present invention relates generally to microphone devices useful, for example, in hearing aid devices. The present invention relates more particularly to tunable microphone devices, and methods used to tune them.
2. Technical Background
Microphone devices generally include a diaphragm that is somewhat flexible and moveable by acoustic force. However, manufacturing diaphragms with well-defined responses is relatively difficult. In particular, nanoscale statistical irregularities caused by the nature of the materials of the diaphragms and manufacturing variations in deposition, lithography, and etch methods lead to significant variation in mass and stiffness. The variations in mass and stiffness, in turn, lead to differences of the responses of the diaphragms and of the microphone elements and devices in which they are used. Moreover, environmental factors such as oxidation, condensation of airborne vapors and contamination can alter the diaphragm after the structure has been fabricated.
Directional microphone devices generally include two or more microphone elements closely matched in response. However, fabrication of closely matched microphone elements can be difficult due to manufacturing variations. Even a small difference in response, e.g., as little as 0.2 dB, can destroy directionality completely. Electronic calibration and compensation can also be used to achieve directionality, but such methods are very complex, require large systems and large power consumption, and lead to high costs. Manually selecting matched microphone elements can provide limited success, but matching involves high cost and requires additional matching after installation of the device.
Directional microphone devices are used, for example, as the basis for hearing aid devices. Hearing aids are, however, not a one-size-fits-all solution to hearing problems. A patient's level or type of hearing impairment and/or physical condition can impact sound delivery within the ear, making a universal fit impossible. Moreover, in order to fully support a wearer's needs, tuning to adjust signal-to-noise ratio and directionality is generally desired. Accordingly, hearing aids must be uniquely tuned for each patient. There currently exist no low-cost, effective methods for in situ tuning.
Accordingly, there remains a need for microphone devices and directional microphone devices with well-defined and tunable response characteristics.